Method of manufacturing a die for duplicating plastics information carriers

ABSTRACT

The invention relates to a method of reproducing plastics record carriers, in particular duplicating video records. According to the invention, a metal die is used which is provided with a thin-liquid molding resin of a particular composition which can be polymerized by radiation. A radiation-pervious substrate which is manufactured from synthetic material, for example polymethylmethacrylate, is provided on the molding resin. The molding resin is exposed to light via the substrate after which the cured molding resin together with the substrate connected thereto is removed from the die. The molding resin used in the process comprises low-molecular monomers or oligomers which contain on an average 25-70% by weight of hydrocarbon groups and/or phenyl groups. The molding resin is aprotic and has a functionality as regards unsaturatedness which is between the values 2 and 6. A suitable molding resin contains mono-, tri- or tetra esters of acrylic acid. The molding resin preferably has a swelling capacity with respect to the substrate and for that purpose preferably comprises a vinylmonomer. The metal die used in the method preferably is a quite flat die which is obtained by providing the master disk which is a flat glass plate with information track with a nickel layer, gluing hereon a flat stiffening plate and then removing the master disk. The resulting father disk may be used as a die. Alternatively, further metal copies may be made herefrom which are provided in a simpler manner with a flat stiffening plate. The invention also extends to the molding resin, substrate and die used in the method, as well as the resulting plastics record carriers.

This is a division of application Ser. No. 95,130 filed Nov. 16, 1979,now U.S. Pat. No. 4,275,091 which is in turn a continuation ofapplication Ser. No. 887,188 filed Mar. 16, 1978 now abandoned whichapplication is in turn a division of application Ser. No. 774,973, filedMar. 7, 1977, and now abandoned.

The invention relates to a method of duplicating plastics informationcarriers in which a polymerizable molding resin is provided on a diecontaining an information track, which resin on the side remote from thedie is provided with a substrate and, after curing of the molding resin,the assembly of molding resin and substrate connected thereto is removedfrom the die.

In this connection the invention concerns preferably the manufacture ofso-called video (optical) records in which the information trackcomprises very fine optical information.

Such a method is known from German Offenlegungsschrift No. 24 43 020.According to this known process which, due to the use of a moldingresin, is briefly termed a molding process, a specially manufacturedsilicone rubber die is used. In another commonly employed process ofmanufacturing plastic video records, the so-called compression moldingprocess, a die manufactured from metal is used.

In order to obtain a better insight of the present invention theabove-mentioned known processes are explained as follows.

A compression molding process for the manufacture of video records whichis analogous to the compression molding process for phonograph recordsconventionally used for years already, is described in the publishedNetherlands Patent Application No. 7212045 filed in the name ofApplicants. In this process a die manufactured from nickel is used whichhas been obtained by first electroless plating and then nickelplating amaster disk, a glass disk having a circular or spiral-like informationtrack of cured photoresist, and then removing the master disk. Theresulting father disk may be used as a die but usually further so-calledfirst copies (mother disk) are made from the father disk byelectrodeposition, then from the mother disks second copies are made,and so on. The last copies are termed dies. When making plastics videorecords the die is pressed on a thermoplastic moulding mass at elevatedtemperature and pressure, said mass consisting, for example, of acopolymer of vinyl chloride and vinyl acetate, after which the assemblyis cooled and, after removing the pressure, the moulded disk is finallyremoved from the die. One of the drawbacks of the compression moldingmethod is that there exists a difference in expansion between the dieand the molded disk during cooling so that undesired stresses occur inthe disk which may result in loss or deformation of the opticalinformation. In addition small particles of the synthetic resin oftenremain adhering to the metal die so that the subsequent copies showdefects. The die becomes either useless or must be cleared. Furthermore,the compression moulding process shows a rather long cycle time andrequires a good deal of energy. Stringent requirements have to beimposed upon the plastic synthetic resin used as regards stability inshape especially in the long run and under considerably varyingclimatological conditions.

In the molding process known from the above-mentionedOffenlegungsschrift a special die is used which is also manufacturedaccording to a molding process. For that purpose the glass master diskis provided with a release agent on which a liquid vulcanizablepolysiloxane (silicone rubber) is provided which contains 10% by weightof catalyst. A second glass plate which is provided on one side with anadhesive, is pressed on the silicone rubber layer with the adhesivelayer lowermost, after which the assembly is cured at elevatedtemperature of 71°-204° C. and finally the master disk is removed.

The resulting die consists of a glass disk which is provided on one sidewith a silicone rubber coating which comprises the information track.For making plastic copies a liquid mixture of polyurethane resin isprepared which consists of polyurethane resin, thinner and catalyst.This mixture is provided on a substrate of Mylar polyester film afterwhich the coated substrate is pressed against the rubber coating of thedie by means of a rolling process. It is alternatively possible first topour the mixture of polyurethane resin on the rubber coating of the dieand then providing the polyester film thereon. The polyurethane resinwith polyester substrate provided on the die is then cured, the curingtime varying from 15 to 45 minutes in accordance with the composition ofthe polyurethane resin. The resulting laminated disk of curedpolyurethane with the polyester film is finally removed physically fromthe die. According to the text of the above-mentionedOffenlegungsschrift, an epoxy resin or acrylic resin may alternativelybe used instead of polyurethane resin. Instead of the Mylar polyesterfilm, a thin and flexible metal foil may alternatively be used. It isfurthermore stated on page 14, third paragraph of theOffenlegungsschrift No. 24 43 020 that monomers which are polymerizableby radiation, as described in the Broadbent patents, may be used. In theBroadbent patents, for example, U.S. Pat. Nos. 3,658,954 and 3,687,664,there is disclosed to a duplicating process for video disk records inwhich a gaseous monomer which can be polymerized with ultraviolet lightis used, for example, acrolein and parylene vapour.

The duplicating process according to the above-mentionedOffelengungsschrift has the following drawbacks. First of all, a veryspecial silicone rubber die has to be manufactured.

In Applicant's opinion, the choice of this particular material is basedon the requirement that the copy has to be easily releasable from thedie. During the manufacture of the silicone rubber die, curing of therubber takes place at elevated temperature. As a result of differencesin thermal expansion between the rubber die and master disk to bemanufactured, small differences in dimension may occur. In particularfor the reproduction of video information in which a very high resolvingpower is required, small differences in dimension may adverselyinfluence the reproduction quality. A further drawback is thecomparatively long curing time of the copy (polyurethane with polyesterfilm) in the die. The curing time may of coarse be reduced by performingthe operations at higher temperatures, but then again the undesireddifferences in thermal expansion play a role which deteriorate thetransfer of video information and furthermore result in thermal stressesin the copy. As a result of said stresses, deformation of the copy andloss or deformation of video information may take place in the course oftime. A further drawback is the restricted stability of the resinmixture. The curing begins as soon as the polyrethane resin has beenadded to the catalyst.

It has furthermore been found that the surface of the silicone rubberdie is apt to be attached by molding resins, in particular thosecontaining polymerizable monomers.

Applicants have now developed a method of duplicating plastic recordcarriers which does not exhibit the above-mentioned drawbacks.

The invention relates more in particular to a method of duplicatingplastics information carriers in which a polymerizable molding resin isprovided on a die provided with an information track which resin, on theside remote from the die, is provided with a substrate and, after curingthe molding resin, the assembly of molding resin and substrate connectedthereto is removed from the die, and is characterized in that a die isused of which at least the surface comprising the information track ismanufactured from metal, a liquid moulding resin which can bepolymerized by radiation is then provided on the metal surface, saidresin containing low molecular monomers and/or oligomers which on anaverage contain from 25 to 70% by weight of saturated hydrocarbon groupsand/or phenyl groups, the molding resin being entirely or substantiallyentirely aprotic and having an average functionality as regardsunsaturatedness which lies between the values 2 and 6 inclusive, inwhich furthermore the molding resin, on the side remote from the die, isprovided with a radiation-pervious substrate, the molding resin is thencured by radiation through the substrate and the polymerized moldingresin together with the substrate connected thereto is then removed fromthe die.

The use of a metal die or a die having a metal surface in the moldingprocess according to the invention is of importance. As already statedabove, metal dies have been used for some time already in compressionmolding processes for the manufacture of video recods and phonographrecords. Much know-how and experience has been built up in the course ofthe years as regards the manufacture and properties of metal dies, whichmakes its use in the molding process according to the invention veryattractive. For example a metal die or a die having a metal surface isgenerally, and in particular at lower temperature, only slightlysensitive to attack by synthetic resins.

However, the use of a metal die in the method according to the inventionis possible only if in combination herewith a special molding resinwhich can be cured by radiation is used and which shows theabovementioned characteristics. Only in that case is the cured resinreadily releasable from the metal die and at the same time it isstrongly bound to the substrate.

Due to the importance of the radiation-curable molding resin, thesubstrate and the die in the method according to the invention, theseelements will now be described in greater detail.

A. LIQUID RADIATION-CURABLE MOLDING RESIN

After providing the liquid molding resin on the metal surface of the dieand providing it with a substrate, the resin is polymerized through thesubstrate by means of radiation, that is to say it is cured. Accordingto the invention, the radiation may be both ultra-violet light having asis known an upper wavelength limit of 3900 Å, and visible light. Thecomposition of the liquid molding resin which can be cured by exposureto U.V. light differs from that which can be cured by means of visiblelight in that a different type of catalyst is used. The catalyst is amaterial which upon exposure to light forms radicals which subsequentlyinitiate the polymerization reaction of the remaining components of themoulding resin. The formation of radicals can be produced by lightabsorption of the catalyst itself but also by light absorption of asensitizer which transfers the absorbed energy to the catalyst. In thecase of a moulding resin which can be cured by U.V. light, an aromaticcarbonyl compound, for example a benzoin derivative, for example,benzoin isobutylether, is often used as a catalyst. In a moulding resinwhich can be cured by means of visible light, a xanthene dye having anamine as an auxiliary material is often used as a catalyst, for example,orythrosin with dimethylamine-ethanol.

Liquid resin compositions which can be cured by radiation are oftenreferred to in literature as "light-curable resins" or"ultra-violet-curable resins". Such a composition generally comprisesone or more polymeric compounds comprising polymerizable groups incombination with polymerizable monomers which also serve as solvents ordiluents. A small quantity of a catalyst, also referred to as aphoto-initiator, is also present. The curing can take place in a shorttime, for example, in 1 to 300 seconds dependent upon the lightintensity. The presence of atmospheric oxygen often extends the requiredcuring time and often results in mechanically and chemically inferiorproducts. The known photosensitive resins are used on an industrialscale for making a protective layer on metal, wood or sometimes onpaper. Rigid, hard layers with a good adhesion are obtained. Inparticular the good adhesion to the abovementioned materials is a highlydesired property for the known application.

In the method according to the present invention, however, aradiation-curable liquid molding resin is used which does not adhere toa metal base, in this case the metal surface of the die.

In addition to this property of non-adhesion to a metal base, themolding resin which is used in the method according to the invention hasthe property of strongly adhering to the substrate surface. Thissubstrate consists of a synthetic resin as will be describedhereinafter.

On the basis of an extensive investigation, Applicants have succeeded indeveloping a new radiation-curable liquid molding resin which shows theabove-mentioned adhesion characteristic. The molding resin furthermorecomprises only few reactive groups after curing which otherwise mightpossibly give rise to a substantial postcuring. Furthermore, the curedresin layer shows such low inner stresses that no tensile or bendingstress is exerted on the substrate. The molding resin also shows a lowviscosity with a viscosity coefficient of almost 100 cP and preferably1-10 cP, so that the application of the molding resin to the die canreadily be carried out without the inclusion of air bubbles.

The invention also relates to this new molding resin which ischaracterized by the following features:

(a) the molding resin comprises low-molecular monomers and/or oligomers,

(b) the monomers and/or oligomers used in the molding resin comprise onan average 25-70% by weight of saturated hydrocarbon radicals and/orphenyl groups,

(c) the molding resin is aprotic or substantially aprotic,

(d) the molding resin has an average functionality as regardsunsaturatedness which is between the values of 2 and 6 inclusive.

These resins may be further characterized as follows.

(ad a) Also in connection in order to obtain a correct degree ofviscosity, the molding resin contains very little polymer, for example,less than 5% by weight. For the same reason, further preference istowards a molding resin which consists mainly, that is for at least 95%,of low-molecular monomers. The term low-molecular in this context meansan average molecular weight of the monomers used which is at mostapproximately 400. The oligomers used generally have a higher molecularweight, for example 500-2000.

(ad b) The said content of saturated hydrocarbons and/or phenyl groupsis related to the desired moderately polar character of the moldingresin after curing. A phenyl group, as well as of course a saturatedhydrocarbon, may be considered to be an apolar group within the scope ofthe invention. It is very well feasible that the molding resin comprisescertain monomers and/or oligomers the content of saturated hydrocarbongroups and/or phenyl groups of which is small. This has to becompensated for by the presence of other monomers and oligomers having acomparatively high content of saturated hydrocarbon radicals and/orphenyl groups such that on an average the above-mentioned percentage byweight of 25-70% is reached over the whole mixture. The average contentof saturated hydrocarbon radicals and/or phenyl groups is preferablybetween 40 and 65% by weight.

(ad c) As a result aprotic character of the molding resin causes thatstarting from the resin no hydrogen bridges with the metal surface ofthe die are formed.

(ad d) The idea of functionality as regards unsaturatedness is describedinter alia in "Principles of Polymer Chemistry, Paul J. Flory, CorneelUniv. press, New York 1953, pages 31-33". In connection with the presentinvention, "average functionality as regards unsaturatedness" is to beunderstood to mean the average number of ##STR1## per moleculemultiplied by the factor two. This notion can be illustrated by a simpleexample of a mixture of 1 grammolecule of ethene (functionality=2) and 1grammolecule of butadiene (functionality=4). The average functionalityas regards unsaturatedness of this mixture is ##EQU1## The factor N×1mentioned in the denominator of the quotient relates to (Avogadronumber) molecules of ethene which comprise per molecule one ##STR2## Thefactor N×2 relates to N molecules of butadiene with two ##STR3## permolecule.

In a preferred form of the molding resin according to the invention theaverage functionality as regards unsaturatedness is between the values2.1 and 3.5 inclusive.

On the basis of the characteristic of the molding resin mentioned abovesub (a) to (d), those skilled in the art can easily prepare a suitablemolding resin.

Very suitable molding resins which have also been used in a preferredform of the invention comprise, in addition to the hereinbeforementioned light sensitive catalyst, thin-liquid mixtures oflow-molecular mono-, di-, tri- or tetra esters of acrylic acid. Suchmolding resins after exposure on the die show no or only little adhesionto the metal surface of the die. The mechanical separation of the diefrom the assembly of the cured molding resin and substrate is easilycarried out. From electron microscope studies it appears that thesurface structure of the die comprising the information to be reproducedis present in the molding resin layer without defects.

Examples of the above-mentioned suitable esters of acrylic acid arebifunctional (functionality=2) monoacrylates, in particularalkylacrylates, phenylacrylate, alkoxyalkylacrylates andphenoxyalkylacrylates. Specific very suitable representatives hereofare, for example, ethylacrylate, n-butylacrylate, i-butylacrylate,hexylacrylate, heptylacrylate, octylacrylate, 2-ethylhexylacrylate,decylacrylate, dodecylacrylate, octadecylacrylate, othoxyethylacrylateand phenoxyethylacrylate. Furthermore tetrafunctional di-acrylates, inparticular alkanedioldiacrylates and alkeneglycoldiacrylates may beemployed. Of these may be mentioned specifically1,3-propanedioldiacrylate, 1,3-butanedioldiacrylate,1,6-hexanedioldiacrylate, 1,10-docanedioldiacrylate,diethyleneglycoldiacrylate, triethyleneglycoldiacrylate,tetraethyleneglycoldiacrylate and tripropyleneglycoldiacrylate. Verysuitable hexafunctional triacrylates are, for example,trimethylolpropanetriacrylate and pentaerythritoltriacrylate.

Example of interesting acrylic acid esters of oligomers arepolyethyleneglycoldiacrylate, polypropyleneglycoldiacrylate,polyesteracrylate, urethaneacrylate, epoxyacrylate and ethoxylatedbisphenol A-diacrylate. Very suitable resin compositions according tothe invention are recorded in the following table.

    __________________________________________________________________________    Resin compositions                                                            moulding                                                                      resin                                                                              Constituents                                                             serial                                                                             difunctional mono-                                                                          polyfunctional                                             no.  acrylate  Wt. %                                                                             acrylate  Wt. %                                                                             initiator                                                                           Wt. %                                  __________________________________________________________________________    1    2-ethylhexylacrylate                                                                    78  1,1,1-trimethylolpro-                                                                   20  benzoiniso-                                                                         2                                                         pane triacrylate                                                                            butylether                                   2    ethylacrylate                                                                           78  1,1,1-trimethylolpro-                                                                   20  benzoiniso-                                                                         2                                                         pane triacylate                                                                             butylether                                   3    phenylacrylate                                                                          78  1,1,1-trimethylolpro-                                                                   20  benzoiniso-                                                                         2                                                         pane triacylate                                                                             butylether                                   4    2-ethoxyethylacry-                                                                      78  1,1,1-trimethylolpro-                                                                   20  benzoiniso-                                                                         2                                           late          pane triacrylate                                                                            butylether                                   5    2-ethoxyethylacry-                                                                      78  pentaerythritol-                                                                        20  benzoiniso-                                       late          tetraacrylate butylether                                   6    octadecyl acrylate                                                                      73  ethylenediacrylate                                                                       8  benzoiniso-                                                                         2                                           ethylacrylate                                                                           17                butylether                                   7    2-ethoxyethylacry-                                                                      78  ethylenediacrylate                                                                      18  benzoiniso-                                                                         2                                           late                        butylether                                   8    2-ethylhexylacry-                                                                       59  butanedioldiacrylate                                                                    19,5                                                                              benzoiniso-                                                                         2                                           late          1,1,1-trimethylolpro-                                                                   19,5                                                                              butylether                                                      pane triacrylate                                           __________________________________________________________________________

The resin layer obtained after curing the molding resin is rather soft,in contrast with the hard layer which is obtained in the knownapplication of U.V. molding resins as a protective layer on metal, woodor paper. It is hence not surprising that the above-mentioned moldingresin compositions as such are not commercialized or recommended.

The surface structure (information track) of the cured resin layeraccording to the invention, however, is nondeformable also when in asubsequent treatment a thin metal layer, for example an Al-layer, isprovided on the information surface, for example, by vapour deposition.Usually a protective lacquer is provided on the metal layer.

B. SUBSTRATE

The substrate which consists of plastics and has the shape of a plate,disk or foil mainly determines the mechanical properties of the plasticsrecord carrier, for example a video disk, to be manufactured. Since themoulding resin is exposed to light via the substrate, the substrateshould be pervious to the type of light used, hence to visible light orto ultra-violet light. The perviousness to visible light isself-evident; transparent or translucent substrate materials are useful.As regards the perviousness to ultra-violet light it may be noted thatmany synthetic resins comprise low-molecular materials such asstabilizers against degradation by sun light. If these low-molecularmaterials absorb U.V. light, a disk or foil of such a synthetic resinmay be less suitable for use as a substrate in combination with aU.V.-curable molding resin. Experiments have proved that a disk or foilshould at least have a transparency degree of 5%, to the relevant typeof light but preferably more than 50%.

In a preferred embodiment of the method according to the invention, afoil, disk or plate is used as a substrate in a thickness between 200 μmand 1.5 mm and which consists of polyvinylchloride/acetate copolymer,polyvinylchloride, polycarbonate, polyester, polystyrene,cellulosetriacetate, celluloseacetobutyrate or mixtures thereof. Such afoil, plate or disk transmits sufficient light, in particular U.V.light, to cure the photosensitive moulding resin.

After exposure through the substrate, the thin layer of cured moldingresin should readily adhere to the substrate. The molding resinaccording to the invention described in detail above readily adheres ingeneral to the above-mentioned plastics. A less than optimum adhesioncan be improved by previously roughening the substrate, for example, bytreating with chloroform. The substrate may also be provided with anadhesive layer or top layer which has a good adhesion to the curedmolding resin. A good adhesive layer in the case of the substrateplexiglass (polymethylmethacrylate) for example, is a coating ofpolyvinylchloride/acetate copolymer. However, such an improvement of theadhesion requires extra treatments of the substrate.

Applicants have found that a good adhesion of the cured moulding resinto the substrate is associated with a certain attack of the substrate bythe uncured molding resin.

In a preferred embodiment of the moulding resin according to theinvention, the molding resin has a swelling capacity with respect to thesubstrate material.

This swelling capacity of the molding resin can be determined in asimple manner by dipping a substrate foil or substrate disk in themoulding resin for a certain period of time, for example, 1 to 6 hours,then removing the disk, drying and determining the increase in weight ofthe disk or foil.

The above-mentioned liquid molding resins on the basis of mono-, di-,tri- or tetra esters of acrylic acid as a rule have sufficient swellingcapacity with respect to the above-mentioned substrate plastics. It hasbeen found experimentally, for example, that a molding resin accordingto the invention which contains 78% by weight of 2-ethylhexylacrylate,20% by weight of trimethylolpropane triacrylate, and 2% by weight ofinitiator, produces an increase in weight of more than 0.5% in foils ofinter alia polyvinylchloride/acetate copolymer, polyvinylchloride andpolystyrene. The dipping time was 6 hours.

With a substrate consisting of polymethylmethacrylate (plexiglass) theadhesion was not optimum when the above-mentioned moulding resin wasused. A plate of plexiglass which had been dipped in the above-mentionedresin for 6 hours hence showed only an increase in weight of less than0.01%. The swelling capacity of the relevant moulding resin with respectto the substrate plexiglass thus is insufficient. In this connection itmay be noted that the reference to sufficient swelling capacity of themoulding resin with respect to the substrate foil or disk is true if thefoil or disk shows an increase in weight of at least 0.1% upon dippingin the resin for 6 hours.

An insufficient swelling capacity of the moulding resin can be improvedby incorporating in a preferred embodiment of the molding resinaccording to the invention at least one component which in itself has asufficient swelling capacity. In a further preferred embodiment of themolding resin, said component is a vinylmonomer. The extra advantage isobtained that the component, upon exposure, also reacts with theremaining constituents of the resin so that a binding of the cured reinto the substrate is obtained. A suitable vinylmonomer is, for example,an alkylacrylate of which the alkyl group contains 2 or 3 carbon atomsor an alkoxy alkylacrylate of which both the alkoxy and the alkyl groupcontains 1 or 2 carbon atoms.

For illustration hereof it is observed that in the above example ofinsufficient adhesion to plexiglass the adhesion was improved byreplacing the 2-ethylhexylacrylate in the resin composition by an equalamount of ethylacrylate. It was established by means of the dipping testthat upon dipping a plate of plexiglass in ethylacrylate the plexiglassshowed an increase in weight of more than 5% after 1 hour.

C. DIE

As already stated above, the metal dies, usually nickel dies, used inthe compression molding process of video disks may be used in a methodaccording to the invention. Such a die is disclosed, for example, in thepreviously mentioned published Netherlands Patent Application No.7212045. A usual process for the manufacture of the metal die consistsin that the master disk, that is a flat glass disk having an informationtrack which usually consists of cured photoresist, is first provided inan electroless manner with a conductive metal layer, for example AG orNl layer, and is then electroplated with a metal layer, for example, anickel layer, after which the glass disk with photoresist is removed.The fatherdisk obtained in this manner may be used as such as a die.Usually, further copies are made by electrodeposition, such as first,second, third copies, and so on, with which a whole family of metalcopies is built up. The first copy made from the fatherdisk is sometimestermed mother disk. The last copies are referred to as dies.

Applicants have found, that although the starting material is a quiteflat master disk, the metal copies produced herefrom show unevenesseswhich are usually small but which, in the compressionless mouldingprocess according to the invention, result in plastics record carrierswhich are not entirely flat. As a result of this the quality of theplastics record carrier is adversely influenced.

It is to be noted that in a compression moulding process theseunevenesses found by Applicants do not play a part because in such aprocess the die during operation is stretched flat on the cooling andheating block of the compression moulding die.

Applicants have observed that the unevenesses are caused in particularby internal stresses which are formed during the metallization in thecopies derived from the master disk.

On the basis of this observation, the die used in a preferred embodimentof the method according to the invention is a substantially flat metalfather disk or a metal copy obtained herefrom by electrodeposition. Theterm "substantially flat" means that the factual macroscopic flatnessdiffers at maximum 10μ from the theoretical flat surface.

Such a die forms part of the present invention as such and is obtainedby providing a master disk, which is a flat glass disk having aninformation track on one side, with a metal layer first in anelectroless manner and then by electrodeposition on the side of theinformation track, providing hereon a flat stiffening disk in anadhering manner, then removing the master disk and, if desired,producing other metal copies by electrodeposition from the resultingflat father disk.

The electroless provision of a metal layer, for example an AG-layer orNI-layer, as well as the electrodeposition of a metal layer, for examplean Ni-layer, is known in the art. Reference may be had to theabovementioned Netherlands Patent Application No. 7212045. It is to benoted that the term "electroless provision" also includes thevapour-deposition or spraying of a metal layer.

As a result of the measures according to the above method in which it isof particular importance that first the flat stiffening disk is providedbefore the master disk is removed, no deformations by internal stressescan occur so that the flatness of the glass master disk is maintained inthe resulting father disk.

As may be derived from the method, the resulting flat father diskconsists of an electroless metal layer in which the information track isprovided, an electrodeposited metal layer on the side of the electrolessmetal layer remote from the information track, and a flat stiffeningdisk connected to the electrodeposited metal layer in an adhesivemanner.

According to the invention, the resulting further copies derived fromthe flat father disk by electrodeposition are preferably provided withthe flat stiffening disk. For this purpose, during the manufacture of afirst copy, the father disk provided with a stiffening disk is providedby electrodeposition with a metal layer, a stiffening disk is thenprovided hereon in an adhesive manner and the father disk is thenremoved. In an identical manner, second copies may be obtained from theresulting copy and herefrom again third copies, and so on.

For the sake of good order it is to be noted that such flat copiesconsist of an electrodeposited metal layer which on one side comprisesthe information track and on the other side is provided with a flatstiffening disk connected thereto in an adhering manner.

As a stiffening disk may be used a rigid and flat metal disk, forexample a disk of copper, nickel or aluminum, or a glass plate. Thethickness of the disk is rather variable; for cost-price considerationsa largest thickness of 10 mm is desired. The minimun thickness will beabout 1 mm dependent on the material. The disk is adhered to the metallayer by means of a layer of glue, for example, a two components glue.Preferably a disk of metal or a metal alloy is used in combination withan electrically conductive adhesive, for example, an adhesive havingdispersed metal particles, the advantage being obtained that during theelectrodeposition manufacture of further metal copies the desiredelectric content is optimum. When a glass disk is used, a layer ofadhesive may be used, if desired, which can be cured by radiation, forexample U.V. light.

As a rule, the provision of a reinforcement disk during manufacturingthe father disk should be carried out at the same temperature as that atwhich the layer of metal is provided on the glass master disk. Thetemperature of the electrodeposition bath used often is above roomtemperature and is, for example, 70° C. If the provision of thereinforcing disk should be carried out at a temperature lower than thatused in the electrodeposition bath, the provided metal layer will shrinkfrom the master disk due to differences in thermal expansion. Inpractice, operation at higher temperature is rather cumbersome and thusless attractive.

In a preferred embodiment of the method of manufacturing the father diskthis drawback does not occur. According to the preferred embodiment afather disk is obtained by providing the glass master disk first in anelectroless manner and then by electrodeposition with a metal layerhaving an overall thickness of at most 150 μm, providing hereon in anadhesive manner the flat stiffening disk at ambient temperature and thenremoving the glass master disk.

With a layer thickness of at most 150 μm, the grown metal layer will notshrink from the master disk not upon cooling either. This implies thatthe connection of the stiffening plate outside the electrodepositionbath takes place at normal ambient temperature, which facilitates thewhole manufacture considerably. In general, the layer thickness of thegrown metal layer will be from 60 to 80 μm.

Upon manufacturing electrodeposited copies of the father disk, shrinkagefrom the metal layer does not occur either with larger thickness of thegrown metal layer, for example, 300-400 μm. This is because there is nodifference in thermal expansion between the metal father disk and themetal copy, such as the mother disk and die. The further copies of thefather disk can consequently be provided with the flat stiffening diskat normal temperature.

The technical performance of the method according to the invention ofduplicating plastics record carriers, for example, the provision of theliquid radiation-curable moulding resin on the die surface and theprovision of the substrate over the molding resin can be realized inseveral ways.

For example, the process may be carried out by means of a turntable. Thedie is laid on the flat horizontal metal disk of the turntable, ofcourse with the information-containing surface uppermost. An excess ofmolding resin, for example 5-10 ml, is evenly provided on the die. Theaddition of the molding resin may be carried out, for example, bypouring it centrally on the die and then causing the molding resin toflow radially over the whole surface of the die by rotation of the die.The substrate foil or substrate plate is placed on the layer of moldingresin in such manner that air inclusion is avoided. If desired, thesubstrate may be pressed with a roller. The assembly is rotated in sucha manner that a part of the molding resin between the die and thesubstrate is flung away and thus the desired thickness of the resinlayer is adjusted, for example, from 1-75 μm. After exposure via thesubstrate to the light of, for example, a high pressure mercury lamp,the finished plastics record carrier may be removed from the die.

On the information-containing side of the resulting video disk areflecting and approximately 300 Å thick Al layer is usually provided byvapour deposition at reduced pressure. A protective coating of, forexample, nitrocellulose lacquer is provided over the Al layer. The diskis finally cut to size and equilibrated after having provided a centralaperture.

In the above example of the technical performance of the molding processaccording to the invention, molding resin and substrate are providedseparately and successively on the die. It is alternatively possible toprovide the substrate in a pre-treatment with a layer of molding resinand to provide this assembly on the surface of the die. The furthertreatment, for example exposure, runs off as in the above-mentionedexample.

The plastics record carrier provided with an Al-layer obtained accordingto the method of the invention is read in the same manner as the knownplastics record carrier obtained by a compression molding process. Thereading takes place by means of a thin beam of light (laser light) whichis directed on to the metal layer and is reflected there. The storedinformation is preferably read or scanned with a light beam which passesthrough the carrier material, is reflected by the Al layer and thenemanates again through the carrier material. In contrast with the knownrecord carrier obtained by a compression molding process, the carriermaterial of the record carrier according to the invention is nothomogeneous but shows a laminated structure of cured molding resin andsubstrate. Herewith an inhomogeneity is introduced into the path to betraversed twice by the light beam. The inhomogeneity is, for example, adifference in index of refraction. It has surprisingly been found thatin spite of this inhomogeneity the plastics record carrier obtainedaccording to the method of the invention can be read through the carriermaterial and produces a qualitatively excellent reproduction of thestored information. This is the more surprising when considering thatthe video signal processed in the information track is based on asurface structure having differences in height of 0.1 to 0.2 μm whichare based on the information.

The invention will now be described in greater detail with references tothe following examples and the accompanying drawing, in which,

FIG. 1 is a cross-sectional view of a master disk having a metal layerand a stiffening plate,

FIG. 2 is a cross-sectional view of a die having a stiffening plate,

FIG. 3 is a cross-sectional view of a plastics record carrier.

EXAMPLES 1. Manufacture of the die

A master disk consisting of a polished flat glass disk which in thedrawing is given reference numeral 1 having thereon a spiral-likeinformation track of cured photoresist 2 is electroless nickel-plated bytreatment with an aqueous nickel salt solution containing NiSO₄ 6H₂ O. Asecond nickel layer 4 is provided in the usual electrodeposition manneron the resulting conductive nickel layer 3 which is approximately 300 åthick. For this purpose the master disk 1,2 with the layer 3 is dippedin an aqueous electrolyte solution contaning nickel sulfamate, boricacid and sodium laurylsulphate. The temperature of the solution is keptat 50° C. A voltage is set up across the electrolyte solution, thenickel layer 3 of the master disk serving as cathode. The voltage isslowly raised, for exmaple 0.1 V per minute, until a current strength ofapproximately 40 å is reached. After the total Ni layer has reached athickness of 60μ with this current strength, the master disk 1,2 withthe nickel peel 3,4 grown thereon is removed from the electrolytesolution, cooled in air to ambient temperature (room temperature), thenwashed with water and dried. A flat and stiff aluminium plate 5 wherebythe factual macroscopic flatness of the surface differs maximally 10μfrom the theoretical flatness is glued to said nickel peel. For gluingis used a two-components adhesive, for example an epoxy adhesive, forexample araldite with an amine as a hardener. Although not strictlynecessary, it is recommendable before gluing the plate 5 to peel 3,4, toslightly roughen the surfaces to be glued, for example by etching. Forexample, the nickel surface may be etched with FeCl₃ and the aluminumsurface with sodium hydroxide solution. After curing the glue the masterdisk is separated mechanically from the nickel peel with glued aluminiumplate. The remainders of photoresist possibly remaining on theinformation-carrying side of the nickel peel are dissolved by treatmentwith isopropylalcohol and methylisobutylketone. The resulting fatherdisk which is shown in FIG. 2 consists of an aluminium plate 6 withnickel peel 7. Said father disk may be used as a die for making plasticscopies. It is also possible to manufacture a family of dies from thefather disk. For this purpose the nickel surface of the father disk isfirst passivated by treatment with an aqueous solution if K₂ CrO₇ andthen a 60μ thick nickel layer is grown hereon by electrodeposition(electrolytically). An Al plate is then provided hereon at roomtemperature in the same manner as described above, after which thefather disk is removed. Further copies (dies) can be manufactured in anidentical manner from the resulting mother disk and are also providedwith a flat aluminium plate.

2. A quantity of 10 ml of a radiation-curable molding resin is providedin the centre of a metal die which is secured horizontally on aturntable and which is provided with a stiffening plate as is shown inFIG. 2.

The compositions of the molding resin which is denoted by a serialnumber in column 1 of the table 11 below is stated in the "table ofresin compositions" recorded in the introductory part of thisspecification. The molding resins referred to by the same serial numberare identical. The composition of the metal die is recorded in column 2of the table II below. The turntable is rotated for a few seconds, thecentrally provided molding resin being distributed over the wholesurface of the die. A circular plate, diameter 340 mm, which ismanufactured from the light-pervious synthetic resin (substrate),recorded in column 3 of table II below, is carefully laid on the dieprovided with molding resin, possibly included air bubbles which arevisible due to the light-pervious plate being removed from the layer ofmolding resin by means of a metal roller. It is to be noted that theplate of light-pervious synthetic material (substrate) is pretreated insome cases before it is provided on the layer of molding resin. Theobject of the pretreatment is to promote the adhesion of resin andplate. The pretreatment, if any, is recorded in column 4 of table II. Inthis column, PVC/PVA means that the plate on the side which is incontact with the resin is provided with a layer ofpolyvinylchloride/polyvinylacetate. The layer PVC/PVA is provided bydisposing on the plate a solution of PVC/PVA in cyclohexanone andethylacetate and centrifuging the plate at approximately 1000 rpm. Theindication chloroform means that the plate has been pretreated withchloroform. Chloroform is poured on the plate and is removed again bycentrifuging. The indication ethylacrylate means that the plate has beenpretreated by dipping in ethylacrylate for 30 seconds.

After providing the plate, the resulting sandwich of die, layer ofmolding resin and plate is rotated at 1000 rpm for approximately 15seconds. The excess of molding resin is removed, a homogeneous andthinner layer of molding resin being obtained. The thickness of theresin layer may vary between 0.2 and 300 μm but preferably is 1-75 μm.

The layer of molding resin is then exposed through the substrate to thelight of a light source, for example, a "500 W water-cooledsuperhigh-pressure mercury lamp" arranged 40 cm above the sandwich or aseries of several "TL20W fluorescent" lamps transmitting mainly light of350 nm. In column 5 of table II below tye type of lamp is recorded,SP500 being the above characterized mercury lamp and TL being the abovefluorescent lamp. The exposure time is recorded in column 6 of table II.After the exposure the resulting plastics record carrier is removed fromthe die. The plastics record carrier is shown in FIG. 3 and consists ofthe cured resin layer 8 having an information track and the plate 9 oflight-pervious synthetic resin secured thereto. The plastic recordcarrier (FIG. 3) is usually provided on the side of theinformation-containing layer of molding resin with a 300 Å thick Allayer (not shown in FIG. 3) which is vapour-deposited in a vacuum bellat a pressure of 10⁻⁴ to 10⁻⁵ Torr. Finally a protective layer oflacquer (not shown in FIG. 3) is provided on the Al layer by pouringnitrocellulose lacquer on the Al layer and then centrifuging theassembly, the nitrocellulose lacquer spreading over the whole Al layeras a thin layer.

                                      TABLE II                                    __________________________________________________________________________    moulding                                                                      region                                  exposure                              serial                       substrate                                                                            light/                                                                            time                                  no.  material die                                                                              material substrate                                                                        pre-treatment                                                                        source                                                                            in sec.                               __________________________________________________________________________    1    electrodep. nickel                                                                        copolymer PVC/PVA                                                                         none   SP500                                                                             90                                    1    "           PVC         none   SP500                                                                             90                                    1    "           polymethylmethacrylate                                                                    PVC/PVA                                                                              SP500                                                                             90                                    1    electrodep. nickel with                                                                   polymethylmethacrylate                                                                    ethylacrylate                                                                        SP500                                                                             60                                         top layer of electro-                                                         less nickel                                                              2    electrodep. nickel with                                                                   polymethylmethacrylate                                                                    none   SP500                                                                             300                                        top layer of electro-                                                         less nickel                                                              3    electrodep. nickel                                                                        polymethylmethacrylate                                                                    none   SP500                                                                             60                                    4    "           polymethylmethacrylate                                                                    none   SP500                                                                             60                                    5    electrodep. nickel with                                                                   polymethylmethacrylate                                                                    chloroform                                                                           TL  120                                        top layer of electro-                                                         less nickel                                                              6    electrodep. nickel                                                                        polymethylmethacrylate                                                                    none   SP500                                                                             60                                    7    "           polycarbonate                                                                             none   SP500                                                                             60                                    7    "           polymethylmethacrylate                                                                    none   SP500                                                                             60                                    7    "           polystyrene none   SP500                                                                             60                                    7    electrodep. nickel with                                                                   polymethylmethacrylate                                                                    none   TL  120                                        top layer of electro-                                                         less nickel                                                              8    electrodep. nickel with                                                                   polymethylmethacrylate                                                                    PVC/PVA                                                                              TL  120                                        top layer of electro-                                                         less nickel                                                              __________________________________________________________________________

What is claimed is:
 1. A method of manufacturing a die particularlyadapted for the manufacture of a plastics information carrier containingan information track readable by an optical beam or similar readingmeans by:(a) directly applying to a metal surface of a rigid,substantially flat die, which surface contains the negative of thedesired information track, a thin layer of a thickness of 0.2-300microns of a light-curable polymerizable liquid having a viscosity offrom 1 to 100 cP and comprising low molecular weight acrylic monomers ora mixture of low molecular weight acrylic monomers and acrylicoligomers, which liquid contains 25-70% by weight of unsaturatedhydrocarbon and/or phenyl groups, has an average functionality in regardto unsaturatedness of between 2.1 and 6, is at least substantiallyaprotic and consists for at least 95% of monomers having a maximumaverage molecular weight of about 400; (b) applying to the exposedsurface of said thin layer of polymerizable liquid a thin light-perviousplastic substrate; (c) exposing said thin layer of polymerizable liquidto light radiation through said substrate for a time sufficient to causesaid thin layer of polymerizable liquid to cure to a solid stateadhering to said substrate thereby producing a laminate of saidsubstrate and said cured layer containing the desired optically readableinformation readily removable from said die without effect on saidlaminate or said die; and (d) removing said laminate from said die, saidmethod comprising providing on one major surface of a flat glass platesaid information track, electrolessly depositing on said surface of saidflat glass plate containing said information track a first metal layerby electroless deposition and then, depositing, by electrodeposition, asecond metal layer on said first metal layer, causing a flat stiffeningplate to adhere to the surface of said second metal layer remote fromsaid first metal layer and removing said glass plate from the firstmetal layer thereby forming a flat father disc having a free metalsurface containing the negative of said information track and suitablefor use as a die.
 2. The method of claim 1 wherein the overall thicknessof the two metal layers is not more than 150 μm.
 3. A substantially flatdie obtained by the method of claim 1, the macroscopic flatness of whichdiffers at a maximum 10 microns from the theoretical flat surface of thedie.